Genetic parameters for production traits and heifer pregnancy in Red Angus cattle

Abstract Text: Heifer pregnancy (HPG) is a prediction of the probability that a female will conceive during her first breeding season, typically at a year of age. An inherent issue in the genetic prediction of HPG is that phenotypes can only be collected on females, which limits the amount of information available. To overcome this, inclusion of correlated traits that can be recorded on both sexes, or fertility traits recorded on males could be used to improve accuracy of HPG predictions. Therefore, the objective of this study was to estimate genetic parameters for HPG, 205-d weight (WW), 160-d post weaning gain (PWG), 365-d weight (YW), and scrotal circumference (SC). The project included records on 142,146 animals from the Red Angus Association of America. (Co)Variance parameters were estimated using multiple, two trait animal models and a REML procedure. Heritability and genetic correlations between HPG and production traits were then calculated. Contemporary group was included as a fixed effect for all analyses, additionally, sex and age of dam were included for BW, WW, PWG, and YW analyses, and the linear effect of age was fit for HPG.  The random effect of animal was used to estimate additive genetic effects for all analyses, the random effect of dam was fit for the WW and YW analyses to estimate maternal effects, and a random, maternal permanent environment effect was included for WW. Heritability estimates were 0.58 ± 0.01, 0.27 ± 0.01, 0.22 ± 0.01, 0.29 ± 0.01, 0.45 ± 0.02, and 0.12 for BW, WW, PWG, YW, SC, and HPG (averaged across all analyses on the underlying scale), respectively. Genetic correlations between HPG and BW (-0.06 ± 0.05), SC (-0.08 ± 0.09), WW maternal (-0.02 ± 0.09), PWG (0.06 ± 0.07), YW maternal (0.00 ± 0.11), had confidence intervals that included or were near zero, suggesting minimal genetic relationship between the traits. Correlations were highest between HPG and WW direct (0.29 ± 0.08) and YW direct (0.21 ± 0.07). These results suggest that Red Angus females with high genetic potential for weight at 205 and 365 days have an increased probability of becoming pregnant during their first breeding season. Additionally, the traits WW or YW could be used to help improve accuracy of HPG genetic predictions.

Keywords: beef cattle, genetic correlation, growth, heifer pregnancy